The present study is the first review of the foliose Parmeliaceae s. lat. lichens from andean and subandean Patagonia and Tierra del Fuego (southern South-America, 37° to 55° S). It covers habitats of Nothofagus forests included in the Subantarctic Province (Antarctic Region) and the shrubby and graminean steppe of the Altoandinean and Patagonic Provinces (Neotropical Region). Six maps of the area are included. The work is based on the study of ca. 500 specimens collected by the author and herbarium collections from ASU, BAFC, BCRU, BM, BP, CHR, CTES, H, LIL, MB, MERL, SI, UPS. All collections have been studied in their morphology, anatomy and Chemistry, including TLC. The delimitation of Parmeliaceae s. lat. is discussed and a diagnosis is given. Forty seven species and two subspecies, included in nineteen different genus are reported. Each genera is characterized and a key to identify the genera is presented, as well as a key to identify species within each genus. Morphological, anatomical and chemical features of each species are given. When new features are decribed, they are illustrated. Taxonomic affinities, ecological behavior and intraspecific variability are discussed. The distribution of each taxa is given. The different habitats and species are illustrated by 92 photographs. Sixteen species are reported for the first time from Argentina, among which one for the first time for the Southern Hemisphere, three for southern-South America and three for the first time outside Australasia. Several synonymies are discussed. Chemical data on Menegazzia species from southern South America are presented for the first time and some collections are considered as possible new species. Biogeographically it was found that only three species are common to the centrally located Buenos Aires Province (Argentina), while two genera, twenty species belonging to twelve genera and three subspecies are shared with Australasia. This data are a further evidence of the resemblance of the cool temperate Nothofagus forests of circumantarctic territories, formerly belonging to Gondwanaland. The work is considered a contribution to the biodiversity of the area, due to the new taxa reported as well as for the intraspecific variability described. It is also considered as a good base to start researches on the use of lichens as bioindicators, as done recently through the evaluation of elemental composition of some Parmeliaceae lichens.